JPH10255762A - Lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium battery excellent in a cycle characteristic wherein it is very little that discharging capacity gradually decreases as a positive electrode material in a positive electrode reacts with a nonaqueous electrolyte and the like in the even that charging and discharging are repeated, in the case of the lithium battery using a complex oxide of lithium and cobalt or nickel as the positive electrode material in the positive electrode. SOLUTION: In a lithium battery using a positive electrode 1 in which layers of a positive electrode material expressed by LiXCo1- YNiYOZ,(0<X<=1.3, 0<=Y<=1, 1.8<=Z<=2.2) are provided on a positive electrode current collector 5, the layers 1a, 1b of the above-mentioned positive electrode material are superimposed plurality on the positive electrode current collector 5, and an atomic ratio of Co in a layer of the positive electrode material standing far from the positive electrode current collector is adapted to be large in comparison with an atomic ratio of Co in a layer of the positive electrode material standing near to the positive electrode current collector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium battery, and more particularly to a lithium battery using a positive electrode having a positive electrode current collector on which a layer of a positive electrode material composed of a composite oxide of lithium, cobalt and nickel is formed. This is to suppress the decrease in the discharge capacity when the discharge is repeatedly performed, and to improve the cycle characteristics.

[0002]

2. Description of the Related Art In recent years, as one of new batteries having high output and high energy density, a high electromotive force lithium battery using a non-aqueous electrolyte using an organic solvent or the like and utilizing the oxidation and reduction of lithium has been used. It was started.

Here, in such a lithium battery, various kinds of materials have been used as a cathode material for the cathode, but there has been a problem that the discharge capacity is not sufficient.

In recent years, in order to improve the discharge capacity of a lithium battery, Japanese Patent Application Laid-Open No.
As disclosed in Japanese Patent Application Publication No. 64-64, a positive electrode using a composite oxide of lithium, cobalt and nickel as a positive electrode material has been developed.

However, in the case of such a lithium battery using the composite oxide of lithium, cobalt and nickel as the positive electrode material, when the charge and discharge are repeatedly performed, the positive electrode material and the above-mentioned nonaqueous electrolyte in the lithium battery are mixed. Has caused a problem that the discharge capacity gradually decreases and the cycle characteristics deteriorate.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in a lithium battery using a composite oxide of lithium, cobalt and nickel as a positive electrode material for a positive electrode.

That is, in the present invention, as described above, in a lithium battery using a composite oxide of lithium, cobalt, and nickel as the positive electrode material of the positive electrode, even when charging and discharging are repeated, It is an object of the present invention to obtain a lithium battery having excellent cycle characteristics, in which the positive electrode material rarely reacts with a non-aqueous electrolyte or the like to gradually reduce the discharge capacity.

[0008]

In the lithium battery according to the present invention, in order to solve the above-mentioned problems, a positive electrode current collector is provided with Li _X Co _{1 -Y} Ni _Y O _Z (0 <X ≦
1.3, 0 ≦ Y ≦ 1, 1.8 ≦ Z ≦ 2.2) In a lithium battery using a positive electrode provided with a layer of a positive electrode material represented by the following formula: A plurality of layers of the material are stacked, and the atomic ratio of Co in the layer of the positive electrode material remote from the positive electrode current collector is increased as compared with the atomic ratio of Co in the layer of the positive electrode material close to the positive electrode current collector. It was.

Here, as in the lithium battery of the present invention, the above-mentioned Li _x Co is added to the positive electrode current collector of the positive electrode.
_1-Y Ni _Y O a layer of a positive electrode material _Z is a plurality of layers laminated, the atomic ratio of Co in the layer of the positive electrode material at the position away from the cathode current collector, the positive electrode material at the position close to the cathode current collector If the atomic ratio is higher than the atomic ratio of Co in the layer of the positive electrode, the ratio of lithium in the layer of the positive electrode material remote from the positive electrode current collector having a high atomic ratio of Co increases at the same potential, and the nonaqueous electrolyte It is considered that the catalytic activity for the decomposition such as the above becomes low. Thus, it is considered that the reaction at the interface between the positive electrode material and the non-aqueous electrolyte is suppressed, the decrease in discharge capacity due to charge and discharge is reduced, and the cycle characteristics of this lithium battery are improved.

Here, when the atomic ratio of Co in the layer of the cathode material at a position away from the cathode current collector increases as described above, a decrease in the discharge capacity due to charging and discharging is suppressed. As shown in item 2, the composition of the positive electrode material in the layer of the positive electrode material farthest from the positive electrode current collector is Li _X Co _{1 -Y} Ni _Y O _Z (0 <X ≦ 1.3, 0 ≦
When a material represented by Y ≦ 0.2, 1.8 ≦ Z ≦ 2.2) is used, a decrease in discharge capacity due to charging and discharging is further suppressed, and cycle characteristics are further improved.

When a layer of a cathode material having an increased Co atomic ratio is provided on the surface farthest from the cathode current collector as described above, if the thickness of the cathode material layer on this surface is small, non-aqueous Since the reaction at the interface with the electrolyte or the like may not be sufficiently suppressed, the thickness of the positive electrode material layer on this surface is preferably 5 μm or more.

In providing a layer of the above-described positive electrode material on the positive electrode current collector, a known conductive agent is added to the positive electrode material. In order to be able to insert and extract lithium efficiently, it is preferable to use graphite having a lattice spacing (d ₀₀₂ ) of 3.37 ° or less on the lattice plane (002).

In the lithium battery according to the present invention, as the positive electrode current collector used for the positive electrode, a current collector composed of a generally used known material can be used. As shown, when this positive electrode current collector made of a material containing aluminum is used, the positive electrode current collector is stable even at a high potential, and the cycle characteristics are further improved.

On the other hand, in the lithium battery of the present invention, as a negative electrode material used for the negative electrode, a known negative electrode active material conventionally used can be used.
For example, in addition to metallic lithium and a lithium alloy, a carbon material such as graphite, coke, and an organic fired body that can occlude and release lithium ions can be used.

As the non-aqueous electrolyte used in the lithium battery according to the present invention, a known non-aqueous electrolyte or solid electrolyte can be used.

In the non-aqueous electrolyte described above, known solvents generally used as the solvent can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, Sulfolane, dimethyl sulfolane, 3-methyl-1,3-oxazolidine-2-
ON, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate,
One or two or more organic solvents such as ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, methyl acetate, and ethyl acetate are combined. They can be used, and it is particularly preferable to use a combination of a cyclic carbonate and a chain carbonate.

As the solid electrolyte, those generally used in the prior art can be used. For example, polyethylene oxide, polypropylene oxide, cross-linked polyethylene glycol diacrylate, cross-linked polypropylene glycol diacrylate, polyethylene glycol methyl ether A polymer electrolyte such as a crosslinked acrylate or a crosslinked polypropylene glycol methyl ether acrylate can be used.

Known solutes can be used as the solute to be added to the nonaqueous electrolyte and the solid electrolyte. For example, lithium trifluoromethanesulfonate L
iCF ₃ SO ₃ , lithium hexafluorophosphate LiP
Lithium compounds such as F ₆ , lithium perchlorate LiClO ₄ , lithium tetrafluoroborate LiBF ₄ , and lithium trifluoromethanesulfonate imide LiN (CF ₃ SO ₂ ) ₂ can be used.

[0019]

EXAMPLES Hereinafter, the lithium battery of the present invention will be described specifically with reference to examples. In the lithium battery of this example, a decrease in discharge capacity when charging and discharging are repeated is suppressed. The improvement of the cycle characteristics will be clarified with reference to a comparative example. The lithium battery according to the present invention is not limited to those shown in the following examples, but can be implemented by appropriately changing the scope of the invention without changing its gist.

(Examples 1 to 10) These Examples 1 to 1
In the case of No. 0, a positive electrode, a negative electrode and a non-aqueous electrolyte prepared as described below were used, and the diameter as shown in FIG.
A flat coin-shaped lithium battery having a thickness of 4.0 mm and a thickness of 3.0 mm was produced.

[Preparation of Positive Electrode] In preparing the positive electrode, LiOH, Co (OH) _2, and Ni (OH) ₂ were mixed at a predetermined molar ratio, and then mixed with each other for 8 minutes.
Firing at 50 ° C. for 20 hours, as shown in Table 1 below,
Various positive electrode materials in which i, Co, and Ni were each in a predetermined molar ratio were produced, and these positive electrode materials were pulverized in an Ishikawa-type rai mortar.

Then, graphite having a lattice spacing (d ₀₀₂ ) of 3.35 ° on the lattice plane (002) as a conductive agent and polyvinylidene fluoride as a binder were added to the powder of each positive electrode material thus ground. Is mixed with an N-methyl-2-pyrrolidone solution, and the above-described positive electrode material, graphite as a conductive agent, and polyvinylidene fluoride as a binder are mixed in 9 parts each.
Each positive electrode mixture having a weight ratio of 0: 6: 4 was prepared.

In these examples, two positive electrode mixtures prepared as described above are used, and two positive electrode mixtures are applied on a positive electrode current collector made of aluminum foil having a thickness of 30 μm. After drying, these were pressed into a disc having a diameter of 20 mm at a pressure of ² t / cm ² and heat-treated at 100 ° C. for 2 hours. As shown in FIG. 5, a first positive electrode layer 1a and a second positive electrode layer 1b each containing a positive electrode material shown in Table 1 are laminated with a thickness shown in the same table, and a second positive electrode layer 1b separated from the positive electrode current collector 5 Each positive electrode 1 in which the atomic ratio of Co in the positive electrode material was larger than the atomic ratio of Co in the positive electrode material of the first positive electrode layer 1a close to the positive electrode current collector 5 was produced.

[Preparation of Negative Electrode] To prepare a negative electrode, a rolled sheet of a lithium-aluminum alloy was punched out into a circular shape to prepare a disc-shaped negative electrode of a lithium-aluminum alloy.

[Preparation of Non-Aqueous Electrolyte] In preparing a non-aqueous electrolyte, a mixed solvent in which propylene carbonate (PC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1 was used. Lithium perchlorate LiClO ₄ was dissolved in the mixed solvent at a rate of 1 mol / l to prepare a non-aqueous electrolyte.

[Preparation of Battery] In preparing a battery, as shown in FIG.
Each of the positive electrodes 1 prepared above was used, and the above-mentioned negative electrode 2 was attached to the negative electrode current collector 6. The electrolytic solution is impregnated, the separators 3 are provided between the respective positive electrodes 1 and the negative electrodes 2, and these are accommodated in a battery case 4 formed of a positive electrode can 4 a and a negative electrode can 4 b. The positive electrode 1 is connected to the positive electrode can 4 a through the negative electrode current collector 6, while the negative electrode 2
Is connected to the negative electrode can 4b, and the positive electrode can 4a and the negative electrode can 4b
Was electrically insulated by an insulating packing 7 to produce each lithium battery.

(Comparative Examples 1 to 4) In these Comparative Examples 1 to 4, as in Examples 1 to 10, Li
Each of the positive electrode mixtures is prepared using various positive electrode materials having a predetermined molar ratio of Co, Ni and Co, respectively. In these comparative examples, as shown in FIG. Each containing the positive electrode material shown in Table 1 below.
Each positive electrode 1 was produced by providing two positive electrode material layers, and the other lithium batteries were produced in the same manner as in Examples 1 to 10 above.

(Comparative Examples 5 and 6) In these Comparative Examples 5 and 6, as in Examples 1 to 10, Li
Each of the positive electrode mixtures was prepared using various positive electrode materials having a predetermined molar ratio of Co, Ni and Co, respectively, and as shown in FIG. First positive electrode layer 1a and second positive electrode layer 1 containing the positive electrode material shown
b was laminated with the thickness shown in the same table to produce each positive electrode 1.

Here, in Comparative Examples 5 and 6, as shown in Table 1 below, contrary to the cases of Examples 1 to 10 above, the second Positive electrode layer 1
b, the atomic ratio of Co in the positive electrode material is
Each lithium battery was manufactured in the same manner as in Examples 1 to 10 except that the atomic ratio of Co in the positive electrode material of the first positive electrode layer 1a close to the above was made smaller.

Each of the lithium batteries of Examples 1 to 10 and Comparative Examples 1 to 6 had a charging current of 1
After charging to a charge end voltage of 4.3 V at mA, the battery was discharged to a discharge end voltage of 2.0 V at a discharge current of 3 mA, and charge / discharge was repeated for 100 cycles with such charge / discharge as one cycle. The initial discharge capacity was measured, and the capacity deterioration rate of each lithium battery after 100 cycles was obtained. The results are shown in Table 1 below.

[0031]

[Table 1]

As is apparent from the results, the second positive electrode separated from the positive electrode current collector 5 has a smaller atomic ratio than the atomic ratio of Co in the positive electrode material of the first positive electrode layer 1 a provided on the positive electrode current collector 5. In each of the lithium batteries of Examples 1 to 10 using the positive electrode 1 in which the atomic ratio of Co in the positive electrode material of the layer 1b was increased, only one positive electrode material layer was provided on the positive electrode current collector 5. In each of the lithium batteries of Examples 1 to 4 and the positive electrode material of the first positive electrode layer 1a in which the atomic ratio of Co in the positive electrode material of the second positive electrode layer 1b remote from the positive electrode current collector 5 is close to the positive electrode current collector 5 Comparative Example 5 in which the atomic ratio of Co in
As compared with each of the lithium batteries of No. 6, the capacity deterioration rate after 100 cycles was significantly reduced.

When the lithium batteries of Examples 1 to 10 are compared, the second positive electrode layer 1b separated from the positive electrode current collector 5
In each of the lithium batteries of Examples 1 to 3, 5 to 9 using the one in which the atomic ratio of Co in the positive electrode material was 0.8 mol or more, the second positive electrode layer 1b separated from the positive electrode current collector 5 The cycle characteristics were further improved as compared with the lithium battery of Example 4 in which the atomic ratio of Co in the positive electrode material was 0.5 mol.

In Example 3 using the same cathode material,
When the lithium batteries of Nos. 7 to 10 were compared, when the thickness of the second positive electrode layer 1b was 5 μm or more, the capacity deterioration rate after 100 cycles was the same and low value. The initial discharge capacity was gradually reduced as the thickness of the layer 1b was increased. For this reason, it is preferable that the thickness of the second positive electrode layer be about 5 to 50 μm.

(Embodiments 11 to 14) These embodiments 11
15 are similar to those of the first embodiment.
LiCo _0.8 Ni _0.2 O is used as a positive electrode material in the positive electrode layer 1a.
₂ and Li as the positive electrode material in the second positive electrode layer 1b.
CoO ₂ was used, and the thickness of the first positive electrode layer 1a was 80 μm, and the thickness of the second positive electrode layer 1b was 20 μm.

On the other hand, as shown in Table 2, in the eleventh embodiment, the positive electrode current collector 5 for laminating the first and second positive electrode layers 1a and 1b is made of SUS instead of aluminum foil. To use the positive electrode current collector 5
In Example 12, in preparing the positive electrode mixture, the above d ₀₀₂ was 3.38 instead of graphite as the conductive agent.
In Example 13, the solvent in the non-aqueous electrolyte was ethylene carbonate (EC) and 1,2-dimethoxyethane (DME).
Example 1 was mixed with a mixed solvent in which
In Example 4, each lithium battery was manufactured in the same manner as in Example 1 except that a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1 was used. did.

For each of the lithium batteries of Examples 11 to 14, the initial discharge capacity and the capacity deterioration rate after 100 cycles were obtained in the same manner as described above. Table 2 shows the results.

[0038]

[Table 2]

As a result, the capacity deterioration rate of the positive electrode in Example 1 using aluminum foil as the positive electrode current collector in the positive electrode after 100 cycles was smaller than that of Example 11 in which the positive electrode current collector was formed of SUS. In addition, the capacity deterioration rate of Example 1 was lower after 100 cycles than that in which coke was used as the conductive agent in the positive electrode.

As for the solvent in the non-aqueous electrolyte, the above Examples 1 and 2 were used. When a mixture of propylene carbonate and dimethyl carbonate or a mixed solvent of ethylene carbonate and dimethyl carbonate is used, the capacity deterioration rate after 100 cycles as shown in
The capacity deterioration rate after 100 cycles was lower than that of a mixed solvent in which dimethoxyethane was mixed or a mixture of propylene carbonate and dimethyl carbonate.

(Embodiments 15 and 16) These Embodiments 1
In Examples 5 and 16, the cases of Examples 1 to 10 described above were used.
Each lithium battery was produced in the same manner as in Examples 1 to 10 except that only the positive electrode was changed.

Here, in Example 15, when producing the positive electrode 1, as shown in FIG. 3, a first positive electrode layer 1a and a second positive electrode layer were formed on a positive electrode current collector 5 made of aluminum foil. 1b and the third positive electrode layer 1c are laminated, and as shown in Table 3 below, LiCo _0.2 Ni _0.8 O ₂ is used as the positive electrode material in the first positive electrode layer 1a, the thickness thereof is set to 60 μm, and the thickness of the second positive electrode layer is reduced to 60 μm. LiCo _0.8 Ni _0.2 O ₂ was used as the positive electrode material in the layer 1b, and the thickness thereof was set to 20 μm.
oO ₂ was used and the thickness was 20 μm.

In Example 16, when producing the positive electrode 1, as shown in FIG. 4, the first positive electrode layer 1a and the second positive electrode layer 1a were formed on the positive electrode current collector 5 made of aluminum foil.
The positive electrode layer 1b, the third positive electrode layer 1c, and the fourth positive electrode layer 1d are laminated, and as shown in Table 3 below, LiCo _0.2 Ni _0.8 O ₂ is used as a positive electrode material in the first positive electrode layer 1a, and LiCo _0.5 Ni _0.5 O ₂ is used as the positive electrode material in the second positive electrode layer 1b and its thickness is set to 20 μm, and LiCo _0.8 Ni _0.2 O ₂ is used as the positive electrode material in the third positive electrode layer 1c. 20 μm, the positive electrode material in the fourth positive electrode layer 1d is L
iCoO ₂ was used and its thickness was set to 20 μm.

Then, for each of the lithium batteries of Examples 15 and 16, the initial discharge capacity and the capacity deterioration rate after 100 cycles were obtained in the same manner as described above, and the results are shown in Table 3 below. Was.

[0045]

[Table 3]

As a result, as shown in Examples 15 and 16, two or more positive electrode layers were stacked on the positive electrode current collector 5,
When the atomic ratio of Co contained in the positive electrode material in the positive electrode layer is increased so as to be away from the positive electrode current collector 5, the capacity deterioration rate after 100 cycles is reduced in the same manner as in each of the above embodiments. A low lithium battery was obtained.

[0047]

As described in detail above, in the lithium battery according to the present invention, a plurality of layers composed of the above-mentioned Li _X Co _{1 -Y} Ni _Y O _Z positive electrode material are laminated on the positive electrode current collector of the positive electrode. In this case, the atomic ratio of Co in the layer of the positive electrode material at a position distant from the positive electrode current collector is such that Co in the layer of the positive electrode material at a position near the positive electrode current collector is
, The reaction between the cathode material and the non-aqueous electrolyte in a layer away from the cathode current collector is suppressed, the decrease in discharge capacity due to charge and discharge is reduced, and cycle characteristics are reduced. Excellent lithium batteries can now be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an internal structure of each lithium battery in an example of the present invention and a comparative example.

FIG. 2 is a schematic sectional view showing a state where two positive electrode layers are stacked on a positive electrode current collector in Examples 1 to 14 and Comparative Examples 5 and 6 of the present invention.

FIG. 3 is a schematic cross-sectional view showing a state in which one positive electrode material layer is provided on a positive electrode current collector in Comparative Examples 1 to 4.

FIG. 4 is a schematic sectional view showing a state where three positive electrode layers are stacked on a positive electrode current collector in Example 15 of the present invention.

FIG. 5 is a schematic sectional view showing a state in which four positive electrode layers are stacked on a positive electrode current collector in Example 16 of the present invention.

[Explanation of symbols]

 1 positive electrode 1a first positive electrode layer 1b second positive electrode layer 1c third positive electrode layer 1d fourth positive electrode layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Nishio, Inventor 2-5-2-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Hiroshi Watanabe 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. The method according to claim 1, wherein the positive electrode current collector comprises Li _X Co _{1 -Y} Ni _Y O _Z
(0 <X ≦ 1.3, 0 ≦ Y ≦ 1, 1.8 ≦ Z ≦ 2.2)
In a lithium battery using a positive electrode provided with a layer of a positive electrode material represented by the formula, a plurality of layers of the above positive electrode material are stacked on the above positive electrode current collector, and a layer of the positive electrode material close to the positive electrode current collector is formed. A lithium battery characterized in that the atomic ratio of Co in the layer of the positive electrode material remote from the positive electrode current collector is larger than the atomic ratio of Co in Example 1. 2. The lithium battery according to claim 1, wherein the composition of the cathode material in the layer of the cathode material farthest from the cathode current collector is Li _X Co _{1 -Y} Ni _Y O _Z (0 <X ≦ 1.
3, 0≤Y≤0.2, 1.8≤Z≤2.2). 3. The lithium battery according to claim 1, wherein the positive electrode current collector in the positive electrode is made of a material containing aluminum.